Vehicle horn

A vehicle horn is a sound-making device in an automobile, truck, or other vehicle. The vehicle operator uses the horn to warn others of the vehicle's approach or presence, or to call attention to some hazard. Automobiles, trucks, ships, and trains are required by law in some countries to have horns. Bicycles in many areas are also legally required to have an audible warning device, but not universally, and not always a horn.

Types

Bicycle

Bicycles often have a classic bulb horn, operated by squeezing a rubber bulb attached to a metal horn. Squeezing the bulb forces air through a steel reed located in the throat of the horn, making it vibrate, producing a single note. The flaring horn matches the acoustic impedance of the reed to the open air, radiating the sound waves efficiently, making the sound louder. Other types of horns used on bicycles include battery-operated horns (sometimes even car horns on 12-volt circuits are incorporated), and small air horns powered by a small can of compressed gas.